In a homodyne receiver, a received Radio Frequency, RF, signal is mixed with a signal from a Local Oscillator, an LO signal, in order to convert it to a baseband signal. The mixing of the LO signal and the RF signal is carried out in a mixer circuit.
A drawback with a homodyne receiver is its sensitivity to interfering signals within the RF bandwidth. Such interfering signals will be converted to baseband level via non-linear elements in the receiver. At the baseband level, the interfering signal will be at the same frequency as “the information signal”, thus ruling out the use of filters in order to remove the interfering signal. Thus, interfering RF signals will degrade the performance of a homodyne receiver.
An interfering RF signal will give rise to second and third order distortion products, defined by means of the so called IIP2 and IIP3, respectively. IIP2 is the so called Input Intercept Point for the second order distortion products, and IIP3 is the so called Input Intercept Point for the third order distortion products. The second and third order distortion products are sometimes also referred to as second and third order distortion terms, or simply second and third order distortion. At baseband, BB, level, of a homodyne receiver, the baseband equivalent output interference power level due to second and third order distortion products, here written as PBB,IIP2 and PBB,IIP3, will be:PBB,IIP2=2*Pinterferer−IIP2+const1 [dBm]  (1)PBB,IIP3=2*Pinterferer+PLOleakage−IIP3+const2 [dBm]  (2)
In (1) and (2) above, the term Pinterferer is the input power at RF level of the interfering signal, and “const1 and const2” are constant terms, which may or may not be the same in both equations.
From (2) above, we also see that for the third order distortion products, PBB,IIP3, the leakage from the LO signal will be of significance.
From (1) and (2) above, we also learn that in order to minimize the adverse effects of second and third order distortion products, a homodyne receiver needs to have high IIP2 and IIP3, since this will give a low baseband equivalent input interference power level as measured in dBm. For the same reason, in the case of third order distortion products, the homodyne receiver should have a low LO leakage.
These demands, i.e. high IP2 and IIP3 as well as low LO leakage, lead to an increase in complexity and power consumption of a homodyne receiver, which is naturally not desirable.